I have the free Research Service after being recommended it by a friend, you do have to register and get sent a weekly newsletter though.

Research Service

Free contended live prices from the LSE (Not on the usual 15min delay)
Available on web, iOS and Android devices
Watch lists and portfolio tracking
Follow the most popular bulletin boards
Price alerts to email and phone
Sync your Google Finance portfolio
Fast and simple to use
Join a community of over 90,000

There is a paid option with access to the Level 2 order book that allows you to trade.